the GAsyncResult that was provided to the callback.
a gsize to get the length of the data read in.
a NUL-terminated byte array with the line that was read in (without the newlines). Set length to a gsize to get the length of the read line. On an error, it will return NULL and error will be set. If there's no content to read, it will still return NULL, but error won't be set.
GException on failure.
2.20
Finish an asynchronous call started by DataInputStream.readLineAsync. Note the warning about string encoding in DataInputStream.readLine applies here as well.